A comparative phenological and genetic diversity analysis of two invasive weeds, camel melon (Citrullus lanatus (Thunb.) Matsum. and Nakai var. lanatus) and prickly paddy melon (Cucumis myriocarpus L.), in inland Australia

The biological attributes of two invasive weed species, prickly paddy melon and camel melon, were studied in different disturbed habitats of the Riverina region, NSW during 2010-2011. Seedlings first germinated in early to mid November 2010, once optimal soil temperatures were achieved. Flowering began in both species, generally 35 to 45 days following seedling establishment. Both species exhibited monoecious tendencies, with production of male flowers rapidly followed by production of both male and female flowers on the same vine. Both species exhibited prolific fruit production at all sites, until senescence occurred, at 150-180 days following establishment. Date of senescence varied among sites and species. Molecular genetic sequences analysis of chloroplast (MatK) and nuclear (G3pdh) genes was used to assay population genetic diversity and to verify species identity of melon species sampled from geographically diverse locations in Australia. Genetic variation within the species was not observed among the Australian populations at either of the assayed genes. This lack of genetic diversity may have resulted from a limited entry by each of the species into Australia and or sustained population bottlenecks following their entry. The absence of genetic diversity among Australian populations in both species provides some indication that future bio-control measures may be applicable across the invasive range of these species. Comparisons with sequences from overseas vouchers indentified the Australian specimens of prickly paddy and camel melon as Cucumis myriocarpus and Citrullus lanatus var. citroides respectively. The latter result is discordant with contemporary herbaria identifications which describe Australian camel melon as Citrullus lanatus var. lanatus.